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The Fluid Compress SOP compresses fluid simulations, usually before saving the data to disk. The compression is generally lossy, in that FLIP particles will be culled below the specified depth, and volume bandwidth is limited by zeroing out values. However, SOPs such as Whitewater Source and Particle Fluid Surface are designed to detect compressed fluid input and regenerate any required missing data.
The typical input of this SOP are:
Particles from a FLIP simulation
surfacefield representing the SDF field of a liquid simulation
Three fields name
vel.zrepresenting the velocity vector field of a fluid simulation.
The primary methods of compression by this operator are:
Particle culling below specified depth.
Partitioning the particles spatially and converting them into packed primitives.
Volume bandwidth limiting and conversion to sparse VDB format.
Flagging the VDB’s to save as 16-bit on disk, further reducing disk space.
This SOP creates several detail attributes indicating that the fluid has been compressed. Several of these are also stored to the info block when written to file, making them accessible through the the File SOP's Info Load mode or the
gstat command line tool. These attributes include:
fluidcompress_volumeband- the Particle and Volume bandwidth respectively.
fluidcompress_particlescompressed- the number of fluid particles before and after compression.
fluidcompress_volumet- the original size and center of the fluid volumes.
For more information, see the Fluid Compression help page in the Fluids chapter.
Particles and surface and velocity volumes from a fluid simulation.
The distance between two particles in the fluid simulation. This parameter should generally reference the same parameter on the FLIP Object of the input simulation.
If enabled, any particles below this depth in the
surface field will be deleted. This
parameter is specified in units of Particle Separation.
If enabled, all particle attributes except those specified here will be deleted.
Input volumes named
vel will be converted to VDB format.
Limit the bandwidth on input
vel volumes beyond the specified distance
from the fluid surface.
This value should ideally be greater than the Foam Depth parameter on any Whitewater Solver nodes used with this data as a source.
vel volume is limited by advecting backwards through time and clearing any values
that do not result in advection to within the Limit Bandwidth of the surface field. If operating at a different timescale you can adjust the parameter here.
The CFL constraint on the advection used for velocity limiting. Lower numbers are more accurate but more expensive.
Velocity values below this speed are assumed to be zero and cleared to save memory.
Write 16-Bit Floats
A flag to specify that when writing to disk that the volumes should be down converted to 16 bit. This does not affect how they are stored in memory.